p53 gene mutations in sequential oral epithelial dysplasias and squamous cell carcinomas

Previous studies of oral cancer have suggested that alterations of the p53 tumour suppressor gene occur early in the precancerous stage of development . However, these observations have been based on cross-sectional assessment of abnormal p53 protein staining by immunohistochemistry and mag not neces sarily reflect gene changes. The purpose of this longitudinal study was to examine the changes in the p53 gene in progressive, sequential epithelial d ysplasias and carcinomas from the oral cavity, The study analysed 24 formal in-fixed, paraffin-embedded tissue biopsies from ten patients with two or m ore temporally distinct lesions from the same site in the oral cavity with the diagnosis of hyperkeratosis, epithelial dysplasia, carcinoma in situ or squamous cell carcinoma. Exons 5-8 of the p53 gene were amplified from gen omic DNA using intronic primers and directly sequenced using fluorescent-la belled primers. Standard immunohistochemistry with the DO7 monoclonal antib ody was used to detect mutant and wild-type p53 protein. Mutations of the p 53 gene were identified in 9 of 24 samples. Eight were missense mutations a nd one occurred at a splice site. In six patients, mutations of the p53 gen e occurred late after the transformation of epithelial dysplasia to carcino ma. In two patients with progressive dysplasia, but who had yet to develop invasive carcinoma, p53 missense mutations occurred at the carcinoma in sit u stage in one case and in a moderate dysplasia in the other. There was an inconsistent relationship between gene mutations and the level of p53 prote in staining by immunohistochemistry. It is concluded that during oral carci nogenesis, p53 gene mutations seem to occur relatively late and are associa ted with transformation to the invasive phenotype. Copyright (C) 2000 John Wiley & Sons, Ltd.